Create a Calculator with the Micro:bit Board

Micro:bit 11-02-26

9 0

Tutorial plan

1- Objective of the project

2- Required Components

3- Circuit Connections of system

4- Micropython program of Micro:bit calculator

Objective of the project

The objective of this project is to design and program a functional calculator controlled by the Micro:bit board, using an I2C LCD display for output and a 4x4 matrix keypad for user input.

This project aims to help learners understand how to interface the Micro:bit with external hardware components, including an LCD display for showing numbers and results, and a matrix keypad for entering mathematical operations. It also develops programming skills in MicroPython (or MakeCode), particularly in handling input scanning, data processing, conditional statements, and arithmetic operations.

By completing this project, students will:

Learn how to connect and configure an I2C LCD display with the Micro:bit.

Understand how a 4x4 matrix keypad works and how to read key presses.

Implement basic arithmetic operations (addition, subtraction, multiplication, and division).

Develop problem-solving skills through embedded system design.

Gain practical experience in combining hardware and software to create a real electronic device.

Overall, this project introduces fundamental concepts of embedded systems, electronics, and programming in an interactive and educational way.

Required Components

1. BBC Micro:bit (Microcontroller)

Micro:bit board

The Micro:bit is a small programmable microcontroller board designed for education. It acts as the main controller (brain) of the calculator.

GPIO Extension Card for Micro:bit

The GPIO expansion card for the Micro:bit card

The GPIO extension card Expands the number of usable input/output pins on the Micro:bit, making it easier to connect multiple components like the keypad and LCD display.

2. 4x4 Matrix Keypad

The 4x4 matrix keypad is used to input numbers and operations.

4. LCD Display with I2C Module

The LCD I2C display is used to show: entered numbers, mathematical operations and calculation results.

5. Breadboard

Breadboard

Breadboard is used for building a non-permanent circuit without soldering.

6. Jumper Wires

Jumper wires

Jumper wires (male-to-male or male-to-female) are used to connect components to the Micro:bit.

Circuit Connections of system

1- Connection of keypad to Micro:bit

4x4 Keypad	Micro:bit
R1	P0
R2	P1
R3	P2
R4	P8
C1	P12
C2	P13
C3	P14
C4	P15

Connection of LCD I2C display to Micro:bit

LCD I2C display	Micro:bit
VCC	5V of GPIO card
GND	GND
SDA	P20
SCL	P19

Micropython program of Micro:bit calculator

This program transforms the Micro:bit into a functional calculator using a 4x4 matrix keypad for input and an I2C LCD display for output.

You need to install this library : i2c_lcd for I2C LCD screen.

from microbit import *
from i2c_lcd import I2cLcd

# ---------- LCD Initialization ----------
# Create an LCD object:
# i2c        -> Micro:bit I2C communication
# 0x27       -> I2C address of the LCD (may vary: 0x27 or 0x3F)
# 4          -> Number of rows
# 20         -> Number of columns
lcd = I2cLcd(i2c, 0x27, 4, 20)

# Clear the LCD screen
lcd.clear()

# Display welcome message
lcd.putstr("Microbit Calculator")
sleep(2000)  # Wait 2 seconds
lcd.clear()

# ---------- Keypad Configuration ----------
# Define row pins
lignes = [pin0, pin1, pin2, pin8]

# Define column pins
colonnes = [pin12, pin13, pin14, pin15]

# Define keypad layout (4x4 matrix)
touches = [
    ['1','2','3','+'],
    ['4','5','6','-'],
    ['7','8','9','*'],
    ['=','0','#','/']
]

# Set all row pins as outputs and keep them HIGH (inactive state)
for l in lignes:
    l.write_digital(1)

# Set all column pins as inputs with internal pull-up resistors
for c in colonnes:
    c.set_pull(c.PULL_UP)

# ---------- Function to Read Pressed Key ----------
def lire_touche():
    # Scan each row
    for i in range(4):
        lignes[i].write_digital(0)  # Activate one row (set LOW)

        # Check each column
        for j in range(4):
            # If a column reads LOW, a key is pressed
            if colonnes[j].read_digital() == 0:
                sleep(300)   # Debounce delay
                lignes[i].write_digital(1)  # Reset row
                return touches[i][j]  # Return pressed key

        lignes[i].write_digital(1)  # Reset row after checking

    return None  # No key pressed


# ---------- Calculation Function ----------
def calculer(expr):
    # Lists to store numbers and operators
    nombres = []
    ops = []
    temp = ""

    # Separate numbers and operators from the expression
    for c in expr:
        if c.isdigit():
            temp += c  # Build multi-digit number
        else:
            nombres.append(float(temp))
            ops.append(c)
            temp = ""

    # Add the last number
    nombres.append(float(temp))

    # First handle multiplication (*) and division (/)
    i = 0
    while i < len(ops):
        if ops[i] == '*' or ops[i] == '/':
            if ops[i] == '*':
                res = nombres[i] * nombres[i+1]
            else:
                res = nombres[i] / nombres[i+1]

            # Replace the two numbers with the result
            nombres[i] = res
            nombres.pop(i+1)
            ops.pop(i)
        else:
            i += 1

    # Then handle addition (+) and subtraction (-)
    resultat = nombres[0]
    for i in range(len(ops)):
        if ops[i] == '+':
            resultat += nombres[i+1]
        elif ops[i] == '-':
            resultat -= nombres[i+1]

    return resultat


# ---------- Main Program ----------
expression = ""  # Stores the current expression

while True:
    touche = lire_touche()  # Read pressed key

    if touche:
        # Clear expression if 'C' is pressed
        if touche == 'C':
            expression = ""
            lcd.clear()

        # If '=' is pressed, calculate result
        elif touche == '=':
            if expression != "":
                try:
                    res = calculer(expression)

                    # Display result on third row
                    lcd.move_to(0, 2)
                    lcd.putstr("= " + str(res))
                    sleep(4000)
                    lcd.clear()

                except:
                    # Display error message if calculation fails
                    lcd.clear()
                    lcd.putstr("Erreur")

                expression = ""

        # Otherwise, add pressed key to expression
        else:
            expression += touche

            # Clear first row before displaying new expression
            lcd.move_to(0, 0)
            lcd.putstr(" " * 20)

            lcd.move_to(0, 0)
            lcd.putstr(expression)

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from microbit import *

from i2c_lcd import I2cLcd

# ---------- LCD Initialization ----------

# Create an LCD object:

# i2c -> Micro:bit I2C communication

# 0x27 -> I2C address of the LCD (may vary: 0x27 or 0x3F)

# 4 -> Number of rows

# 20 -> Number of columns

lcd = I2cLcd(i2c, 0x27, 4, 20)

# Clear the LCD screen

lcd.clear()

# Display welcome message

lcd.putstr("Microbit Calculator")

sleep(2000) # Wait 2 seconds

lcd.clear()

# ---------- Keypad Configuration ----------

# Define row pins

lignes = [pin0, pin1, pin2, pin8]

# Define column pins

colonnes = [pin12, pin13, pin14, pin15]

# Define keypad layout (4x4 matrix)

touches = [

['1','2','3','+'],

['4','5','6','-'],

['7','8','9','*'],

['=','0','#','/']

]

# Set all row pins as outputs and keep them HIGH (inactive state)

for l in lignes:

l.write_digital(1)

# Set all column pins as inputs with internal pull-up resistors

for c in colonnes:

c.set_pull(c.PULL_UP)

# ---------- Function to Read Pressed Key ----------

def lire_touche():

# Scan each row

for i in range(4):

lignes[i].write_digital(0) # Activate one row (set LOW)

# Check each column

for j in range(4):

# If a column reads LOW, a key is pressed

if colonnes[j].read_digital() == 0:

sleep(300) # Debounce delay

lignes[i].write_digital(1) # Reset row

return touches[i][j] # Return pressed key

lignes[i].write_digital(1) # Reset row after checking

return None # No key pressed

# ---------- Calculation Function ----------

def calculer(expr):

# Lists to store numbers and operators

nombres = []

ops = []

temp = ""

# Separate numbers and operators from the expression

for c in expr:

if c.isdigit():

temp += c # Build multi-digit number

else:

nombres.append(float(temp))

ops.append(c)

temp = ""

# Add the last number

nombres.append(float(temp))

# First handle multiplication (*) and division (/)

i = 0

while i < len(ops):

if ops[i] == '*' or ops[i] == '/':

if ops[i] == '*':

res = nombres[i] * nombres[i+1]

else:

res = nombres[i] / nombres[i+1]

# Replace the two numbers with the result

nombres[i] = res

nombres.pop(i+1)

ops.pop(i)

else:

i += 1

# Then handle addition (+) and subtraction (-)

resultat = nombres[0]

for i in range(len(ops)):

if ops[i] == '+':

resultat += nombres[i+1]

elif ops[i] == '-':

resultat -= nombres[i+1]

return resultat

# ---------- Main Program ----------

expression = "" # Stores the current expression

while True:

touche = lire_touche() # Read pressed key

if touche:

# Clear expression if 'C' is pressed

if touche == 'C':

expression = ""

lcd.clear()

# If '=' is pressed, calculate result

elif touche == '=':

if expression != "":

try:

res = calculer(expression)

# Display result on third row

lcd.move_to(0, 2)

lcd.putstr("= " + str(res))

sleep(4000)

lcd.clear()

except:

# Display error message if calculation fails

lcd.clear()

lcd.putstr("Erreur")

expression = ""

# Otherwise, add pressed key to expression

else:

expression += touche

# Clear first row before displaying new expression

lcd.move_to(0, 0)

lcd.putstr(" " * 20)

lcd.move_to(0, 0)

lcd.putstr(expression)

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Create a Calculator with the Micro:bit Board

Tutorial plan

1- Objective of the project

2- Required Components

3- Circuit Connections of system

4- Micropython program of Micro:bit calculator

Objective of the project

Required Components

Circuit Connections of system

Micropython program of Micro:bit calculator

0 comment

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